Body mass index (BMI) and risk of noncardiac postoperative medical complications in elderly hip fracture patients: a population-based study

Background: Obese patients are thought to be at higher risk of postoperative medical complications. We determined whether body mass index (BMI) is associated with postoperative in-hospital noncardiac complications following urgent hip fracture repair.

Methods: We conducted a population-based study of Olmsted County, Minnesota, residents operated on for hip fracture in 1988 to 2002. BMI was categorized as underweight (<18.5 kg/m2), normal (18.5-24.9 kg/m2), overweight (25.0-29.9 kg/m2), and obese (> or = 30 kg/m2). Postoperative inpatient noncardiac medical complications were assessed. Complication rates were estimated for each BMI category and overall rates were assessed using logistic regression modeling.

Results: There were 184 (15.6%) underweight, 640 (54.2%) normal, 251 (21.3%) overweight, and 105 (8.9%) obese hip fracture repairs (mean age, 84.2 +/- 7.5 years; 80% female). After adjustment, the risk of developing an inpatient noncardiac complication for each BMI category, compared to normal BMI, was: underweight (odds ratio [OR], 1.33; 95% confidence interval [CI], 0.95-1.88; P = 0.10), overweight (OR, 1.01; 95% CI, 0.74-1.38; P = 0.95), and obese (OR, 1.28; 95% CI, 0.82-1.98; P = 0.27). Multivariate analysis demonstrated that an ASA status of III-V vs. I-II (OR, 1.84; 95% CI, 1.25-2.71; P = 0.002), a history of chronic obstructive pulmonary disease (COPD) or asthma (OR, 1.58; 95% CI, 1.18-2.12; P = 0.002), male sex (OR, 1.49; 95% CI, 1.10-2.02; P = 0.01), and older age (OR, 1.05; 95% CI, 1.03-1.06; P < 0.001) contributed to an increased risk of developing a postoperative noncardiac inpatient complication. Underweight patients had higher in-hospital mortality rates than normal BMI patients (9.3 vs. 4.4%; P = 0.01).

Conclusions: BMI has no significant influence on postoperative noncardiac medical complications in hip-fracture patients. These results attenuate concerns that obese or frail, underweight hip-fracture patients may be at higher risk postoperatively for inpatient complications.